The increasing recourse to renewable energy sources such as solar and wind has led to a need to store the produced energy. For this, hydro-pneumatic storage systems have been developed wherein energy is stored by compressing a gas and is released by gas expansion.
In order to provide good power quality and flexibility to these storage systems, it has been proposed to associate a main storage system (in particular a hydro-pneumatic storage system) with an auxiliary, supercapacitive storage system. Power variation is achieved by intermittent operation of the main storage system and use of the supercapacitive storage system to smooth the resulting power, through the regulation of a common DC bus voltage. Such hybrid storage systems are compatible with a wide range of load and source powers, thanks to the obtained power flexibility.
A cost comparison shows that in addition to its environmental advantages, hydro-pneumatic storage is cost-effective compared to lead acid battery storage. However, further improvements in efficiency are needed.
Theoretical considerations make it desirable to compress and expand the gas under approximately isothermal conditions, but this is not easy to achieve in practice.
A dedicated energy storage solution is also needed to enhance offshore and onshore electric power generation systems, fed by renewable energy sources, such as wind and solar sources.